1. Technical Field
The present invention relates to a photo-curable ink jet ink set and an ink jet recording method using the ink set.
2. Related Art
Various techniques are applied to recording processes for forming images on a recording medium, such as paper, according to image data signals. Among such techniques is an ink jet technique in which images are formed directly on a recording medium by ejecting an ink only onto desired image portions, using an inexpensive apparatus. In the ink jet technique, inks are efficiently used, and accordingly running cost can be reduced. In addition, little noise is produced when the ink jet technique is used, and the ink jet technique is thus advantageous as a recording method.
In order to form characters and images with high fastness to water, solvents, rubbing and so forth on the surface of a recording medium, photo-curable inks that can be cured by being irradiated with light (ultraviolet light) have been used in recent years.
Also, a recording technique performed by overcoating various photo-curable inks one after another is widely used. For example, a color image may be formed by applying different color inks of cyan (C), magenta (M), yellow (Y), black (K), white (W) and other colors one on top of another, or a clear and colorless ink may be applied to the surface of a color image to protect the color image or to give gloss to the color image. For these cases, a technique for forming images having desired quality is desired.
For example, JP-A-2006-181801 discloses an overcoating method using energy ray-curable ink jet recording ink compositions. In this method, a printed coating is formed on a recording member using an energy ray-curable ink jet recording color ink composition (Ia) having a surface tension Sa (mN/m), and then the coating of the color ink is coated with a clear coating of an energy-ray curable ink jet recording clear ink composition (Ib) having a surface tension Sb (mN/m). In this instance, the surface tensions of ink composition Ia, which is applied as an undercoat, and ink composition Ib, which is applied as an overcoat, satisfy the relationships: 31.5≦Sa<35.0 or 27.0≦Sa<31.5, and Sb<Sa.
However, in the method disclosed in the above-cited patent document, when the clear ink composition is applied over the color ink coating that has been applied as an undercoat, the line width of the clear ink becomes very small. Thus, the clear ink composition cannot wet the surface or spread sufficiently.